Disease: Bird Flu (Avian Influenza, Avian Flu)

Bird flu (avian flu) facts

  • Bird flu (avian flu or avian influenza) refers to strains of influenza that primarily affect wild and domesticated birds. Bird flu is named H or N depending on the proteins found on the surface of the virus.
  • Bird flu symptoms include
    • fever,
    • cough,
    • sore throat,
    • nausea.
  • Symptoms often progress to
    • severe breathing problems,
    • pneumonia,
    • acute respiratory distress syndrome (ARDS).
  • Although bird flu is contagious and spreads easily among birds, it is uncommon for it to be transmitted to humans.
  • In the late 1990s, a new strain of bird flu arose which was unusually severe ("highly pathogenic"), resulting in the deaths of hundreds of millions of birds, including poultry.
  • Risk factors for people to contract bird flu include association with birds and poultry farms and bird feces. There have been isolated cases of human-to-human transmission.
  • Definitive diagnosis requires identification of the viral strain by immunological tests.
  • Treatment may include antiviral medication and often requires intensive supportive care.
  • Control efforts, including culling infected flocks and vaccinating healthy birds, have limited the spread of highly pathogenic bird flu strains.
  • In 2011, a mutated strain of highly pathogenic bird flu appeared, H5N1, which is concerning because the existing poultry vaccines are not very effective against the H5N1 strain. In 2013, a new strain, H7N9, appeared in China; other strains are rare.
  • Human infection with highly infectious strains of bird flu is uncommon, with most infections occurring after exposure to infected birds or their droppings.
  • There is no commercially available vaccine for humans against bird flu strains. Human infection with H5N1 bird flu is fatal in approximately 55% of infected humans and 37% infected with H7N9, but only a relatively small number of humans worldwide have become infected since 1997 (H5N1 = 784 people infected and H7N9 = 622).
  • The prognosis of bird flu is fair to poor because of frequent complications and high death rates.

What is bird flu?

Bird flu (avian influenza) is a disease caused by strains of influenza virus that primarily affects birds. In the late 1990s, a new strain of bird flu arose that was remarkable for its ability to cause severe disease and death, especially in domesticated birds such as ducks, chickens, or turkeys. As a result, this strain was called highly pathogenic (meaning very severe and contagious) avian influenza and termed H5N1.

A relatively new strain of bird flu has been identified in China. The influenza A virus is termed H7N9 (H7N9 Chinese bird flu). The identification of the virus (H7N9) was reported Mar. 31, 2013; the new strain is antigenically different from the H5N1 bird flu virus. Unfortunately, the H7N9 strain of bird flu seems to be genetically unstable. Since its discovery in 2013, at least 48 different subtypes of H7N9 have been identified. Because some H7N9 viruses are persistent in some chicken flocks in China, researchers are concerned that the strains will continue to swap genes with other flu viruses and may start a new pandemic.

Since the identification of highly pathogenic influenza, infected birds have been found in Asia, Europe, the Middle East, and Africa. Careful control measures, including destroying infected flocks and vaccinating healthy birds, have reduced the number of cases, but the virus continues to exist in poultry flocks in areas of Asia and Africa. In 2007-2008, there were small outbreaks in Bangladesh and Pakistan due to infected domestic chicken flocks.

In March 2015 in Arkansas and Missouri, the U.S. Department of Agriculture detected bird flu (H5N2) in several flocks of turkeys, including flocks used to produce the popular Butterball turkeys. This has resulted in a number of countries banning U.S. poultry products and is likely to have a significant effect on U.S. poultry exports.

Similarly, the Dutch poultry industry has been affected by the spread of bird flu in chickens in March 2015. Most experts agree that commercial poultry become infected with bird flu due to contamination by wild bird feces.

As of March 2015, no bird flu infections have been reported in humans in the U.S. Although the H1N1 "swine flu" pandemic strain contained some bird flu genes, it was not the same strain as the original H5N1 bird flu.

The virus spreads through infected birds shedding the virus in their saliva, nasal secretions, and droppings. Healthy birds get infected when they come into contact with contaminated secretions or feces from infected birds. Contact with contaminated surfaces such as cages might also allow the virus to transfer from bird to bird. Symptoms in birds range from mild drops in egg production to failure of multiple major organs and death.

The first human case of illness from highly pathogenic avian influenza (termed HPAI in older literature) was identified in 1997. Since that time, H5N1 has infected 784 individuals with 429 deaths. Human cases of highly pathogenic bird flu have been largely confined to Southeast Asia and Africa. Mutations often occur in the virus, and it is possible that some mutations could create a more contagious virus that could cause a regional epidemic or a worldwide pandemic of bird flu among humans. Fortunately, the mutations that have occurred to date have not made the virus more contagious, although the concern remains. The identification of H7N9 bird flu strain is worrisome. However, four people in China (two in Shanghai, one in Nanjing, and one in Anhui province) have been identified as being infected with H7N9; two have died. Health officials worldwide are concerned because of the possibility of a bird flu type that could develop easy transmission from birds to humans. Although easy transmission between humans has not yet developed, H7N9 avian influenza virus has infected 622 individuals; 227 of these individuals died from infection to date. The majority of these infections were due to exposure to infected birds or their droppings.

What causes bird flu?

Bird flu is caused by strains of the influenza virus that have evolved to be specially adapted to enter avian cells. There are three main types of influenza: A, B, and C. The virus that causes bird flu is influenza A type with eight RNA strands that make up its genome. Influenza viruses are further classified by analyzing two proteins on the surface of the virus. The proteins are called hemagglutinin (H) and neuraminidase (N). There are many different types of hemagglutinin and neuraminidase proteins. For example, the recent pathogenic bird flu virus has type 5 hemagglutinin and type 1 neuraminidase. Thus, it is named "H5N1" influenza A virus. The 2013 virus has different surface proteins, H7 and N9, hence the name H7N9. Other bird flu types include H7N7, H5N8, H5N2, and H9N2.

There are many types of influenza viruses, and most prefer to live in a limited number of animals. Thus, swine flu primarily infects swine, and bird flu primarily infects birds. Human influenza strains are best adapted to humans. A few cases may occur in an accidental host, such as when people who have extensive contact with sick birds get the bird flu. In addition to humans and birds, we know that pigs, tigers, leopards, ferrets, and domestic cats and dogs can sometimes be infected with avian influenza viruses.

Influenza viruses mutate easily and often. These mutations can arise spontaneously in a single virus or can occur when two different influenza strains get close enough together to exchange genetic material. There are two major types of mutations in influenza viruses: antigenic shifts, where large RNA segments are interchanged between different influenza virus type, and antigenic drifts, where small RNA sequences are changed. The antigenic shifts are usually responsible for developing new strains. For example, the 2009 swine flu pandemic was caused by a virus that included genetic material from pig influenza, avian influenza, and human influenza strains. New mutations can allow the virus to evade the body's immune system and makes older vaccines ineffective. In 2011, one strain of the highly pathogenic avian influenza virus mutated in this way, making the existing vaccine used against avian flu ineffective against the new strain. Sometimes a flu virus will mutate in a way that makes it able to infect a new species.

Serious pandemic influenza occurs when a relatively new strain of the influenza virus arises that is highly contagious to humans. The most deadly pandemic in modern history was the 1918 influenza, also known as the Spanish flu (although it did not originate in Spain). The 1918 virus spread rapidly and killed tens of millions of people worldwide. Mortality was especially high in healthy young adults. Although the 1918 virus was a human influenza virus, it had many genes that likely came from a strain of bird flu. One reason health officials carefully watch for and try to limit human contact with birds that develop avian flu is to avoid chances for a new strain to arise that may prefer to develop in human tissue.

What are risk factors for bird flu?

Humans may get bird flu from contact with infected birds (chickens, for example) or their infected droppings and secretions. Risk factors include caring for sick birds, killing sick birds, and preparing sick birds for consumption. Despite the large number of people who have contact with poultry every day in the world, human cases of bird flu remain rare. This highlights how difficult it is for the bird flu virus to infect human cells, but mutations like antigenic shifts may reduce such difficulties. The H1N1 pandemic that started in Mexico is an example of such a mutation (swine flu to human flu).

Although direct contact with sick poultry poses the highest risk for bird flu, indirect exposure to bird feces or other materials such as bird eggs is also a risk. Contact with unwashed eggs from sick birds or water contaminated by poultry feces poses a potential risk of disease.

Human-to-human spread has occurred in isolated cases. Thus, caring for a person infected with bird flu is also a risk factor for the disease. There is a theoretical risk in laboratory workers who handle the avian flu virus. One alleged incident in 2009 occurred when a company inadvertently sent live avian flu virus samples to research laboratories, which subsequently were used to vaccinate ferrets. The contaminated vaccine did not result in any human infections.

What are bird flu symptoms and signs?

Symptoms occur approximately two to eight days after exposure, on average. Infected people experience typical flu-like symptoms that may include

  • fever (above 38 C or 100.4 F),
  • cough (usually dry or nonproductive of sputum),
  • sore throat,
  • muscle aches,
  • nausea,
  • vomiting,
  • diarrhea,
  • headache,
  • joint pain,
  • lethargy,
  • nasal secretions (runny nose),
  • insomnia,
  • eye infections.

Children get similar symptoms. This viral infection can progress to pneumonia and even respiratory failure. Bird flu causes a very aggressive form of pneumonia (acute respiratory distress syndrome or ARDS) that is often fatal.

How do physicians diagnose bird flu?

Routine tests for human influenza A will be positive in patients with bird flu but are not specific for the avian virus. To make a specific diagnosis of bird flu, specialized tests are needed. In the United States, local health departments and the Centers for Disease Control and Prevention (CDC) can provide access to the specialized testing. The virus can be detected in sputum by several methods, including culture or polymerase chain reaction (PCR). Cultures should be done in laboratories that have an appropriate biosafety certification. PCR detects nucleic acid from the influenza A virus. Specialized PCR testing is available in reference laboratories to identify avian strains; the CDC is a primary source for available tests for the newest strains of bird flu and can identify the specific type of virus (for example, H5N1 or H7N9).

During and after infection with bird flu, the body makes antibodies against the virus. Blood tests can detect these antibodies, but this requires one sample at the onset of disease and another sample several weeks later. Thus, results are usually not available until the patient has recovered or died.

What is the treatment for bird flu?

Because of the small number of human cases, it has not been possible to conduct rigorous treatment trials for bird flu. The CDC suggests the best way to prevent bird flu is to avoid exposure whenever possible to birds and their feces. People are advised not to touch any ill appearing or dead birds. The CDC and the World Health Organization (WHO) currently recommend oseltamivir (Tamiflu) and zanamivir (Relenza) for the treatment and prevention of avian influenza a viruses. The U.S. government is currently stockpiling H5N1 vaccine in case the virus begins easy person-to-person transmission. Currently, there is no vaccine to protect against H7N9 types of bird flu.

What is bird flu?

Bird flu (avian influenza) is a disease caused by strains of influenza virus that primarily affects birds. In the late 1990s, a new strain of bird flu arose that was remarkable for its ability to cause severe disease and death, especially in domesticated birds such as ducks, chickens, or turkeys. As a result, this strain was called highly pathogenic (meaning very severe and contagious) avian influenza and termed H5N1.

A relatively new strain of bird flu has been identified in China. The influenza A virus is termed H7N9 (H7N9 Chinese bird flu). The identification of the virus (H7N9) was reported Mar. 31, 2013; the new strain is antigenically different from the H5N1 bird flu virus. Unfortunately, the H7N9 strain of bird flu seems to be genetically unstable. Since its discovery in 2013, at least 48 different subtypes of H7N9 have been identified. Because some H7N9 viruses are persistent in some chicken flocks in China, researchers are concerned that the strains will continue to swap genes with other flu viruses and may start a new pandemic.

Since the identification of highly pathogenic influenza, infected birds have been found in Asia, Europe, the Middle East, and Africa. Careful control measures, including destroying infected flocks and vaccinating healthy birds, have reduced the number of cases, but the virus continues to exist in poultry flocks in areas of Asia and Africa. In 2007-2008, there were small outbreaks in Bangladesh and Pakistan due to infected domestic chicken flocks.

In March 2015 in Arkansas and Missouri, the U.S. Department of Agriculture detected bird flu (H5N2) in several flocks of turkeys, including flocks used to produce the popular Butterball turkeys. This has resulted in a number of countries banning U.S. poultry products and is likely to have a significant effect on U.S. poultry exports.

Similarly, the Dutch poultry industry has been affected by the spread of bird flu in chickens in March 2015. Most experts agree that commercial poultry become infected with bird flu due to contamination by wild bird feces.

As of March 2015, no bird flu infections have been reported in humans in the U.S. Although the H1N1 "swine flu" pandemic strain contained some bird flu genes, it was not the same strain as the original H5N1 bird flu.

The virus spreads through infected birds shedding the virus in their saliva, nasal secretions, and droppings. Healthy birds get infected when they come into contact with contaminated secretions or feces from infected birds. Contact with contaminated surfaces such as cages might also allow the virus to transfer from bird to bird. Symptoms in birds range from mild drops in egg production to failure of multiple major organs and death.

The first human case of illness from highly pathogenic avian influenza (termed HPAI in older literature) was identified in 1997. Since that time, H5N1 has infected 784 individuals with 429 deaths. Human cases of highly pathogenic bird flu have been largely confined to Southeast Asia and Africa. Mutations often occur in the virus, and it is possible that some mutations could create a more contagious virus that could cause a regional epidemic or a worldwide pandemic of bird flu among humans. Fortunately, the mutations that have occurred to date have not made the virus more contagious, although the concern remains. The identification of H7N9 bird flu strain is worrisome. However, four people in China (two in Shanghai, one in Nanjing, and one in Anhui province) have been identified as being infected with H7N9; two have died. Health officials worldwide are concerned because of the possibility of a bird flu type that could develop easy transmission from birds to humans. Although easy transmission between humans has not yet developed, H7N9 avian influenza virus has infected 622 individuals; 227 of these individuals died from infection to date. The majority of these infections were due to exposure to infected birds or their droppings.

What causes bird flu?

Bird flu is caused by strains of the influenza virus that have evolved to be specially adapted to enter avian cells. There are three main types of influenza: A, B, and C. The virus that causes bird flu is influenza A type with eight RNA strands that make up its genome. Influenza viruses are further classified by analyzing two proteins on the surface of the virus. The proteins are called hemagglutinin (H) and neuraminidase (N). There are many different types of hemagglutinin and neuraminidase proteins. For example, the recent pathogenic bird flu virus has type 5 hemagglutinin and type 1 neuraminidase. Thus, it is named "H5N1" influenza A virus. The 2013 virus has different surface proteins, H7 and N9, hence the name H7N9. Other bird flu types include H7N7, H5N8, H5N2, and H9N2.

There are many types of influenza viruses, and most prefer to live in a limited number of animals. Thus, swine flu primarily infects swine, and bird flu primarily infects birds. Human influenza strains are best adapted to humans. A few cases may occur in an accidental host, such as when people who have extensive contact with sick birds get the bird flu. In addition to humans and birds, we know that pigs, tigers, leopards, ferrets, and domestic cats and dogs can sometimes be infected with avian influenza viruses.

Influenza viruses mutate easily and often. These mutations can arise spontaneously in a single virus or can occur when two different influenza strains get close enough together to exchange genetic material. There are two major types of mutations in influenza viruses: antigenic shifts, where large RNA segments are interchanged between different influenza virus type, and antigenic drifts, where small RNA sequences are changed. The antigenic shifts are usually responsible for developing new strains. For example, the 2009 swine flu pandemic was caused by a virus that included genetic material from pig influenza, avian influenza, and human influenza strains. New mutations can allow the virus to evade the body's immune system and makes older vaccines ineffective. In 2011, one strain of the highly pathogenic avian influenza virus mutated in this way, making the existing vaccine used against avian flu ineffective against the new strain. Sometimes a flu virus will mutate in a way that makes it able to infect a new species.

Serious pandemic influenza occurs when a relatively new strain of the influenza virus arises that is highly contagious to humans. The most deadly pandemic in modern history was the 1918 influenza, also known as the Spanish flu (although it did not originate in Spain). The 1918 virus spread rapidly and killed tens of millions of people worldwide. Mortality was especially high in healthy young adults. Although the 1918 virus was a human influenza virus, it had many genes that likely came from a strain of bird flu. One reason health officials carefully watch for and try to limit human contact with birds that develop avian flu is to avoid chances for a new strain to arise that may prefer to develop in human tissue.

What are risk factors for bird flu?

Humans may get bird flu from contact with infected birds (chickens, for example) or their infected droppings and secretions. Risk factors include caring for sick birds, killing sick birds, and preparing sick birds for consumption. Despite the large number of people who have contact with poultry every day in the world, human cases of bird flu remain rare. This highlights how difficult it is for the bird flu virus to infect human cells, but mutations like antigenic shifts may reduce such difficulties. The H1N1 pandemic that started in Mexico is an example of such a mutation (swine flu to human flu).

Although direct contact with sick poultry poses the highest risk for bird flu, indirect exposure to bird feces or other materials such as bird eggs is also a risk. Contact with unwashed eggs from sick birds or water contaminated by poultry feces poses a potential risk of disease.

Human-to-human spread has occurred in isolated cases. Thus, caring for a person infected with bird flu is also a risk factor for the disease. There is a theoretical risk in laboratory workers who handle the avian flu virus. One alleged incident in 2009 occurred when a company inadvertently sent live avian flu virus samples to research laboratories, which subsequently were used to vaccinate ferrets. The contaminated vaccine did not result in any human infections.

What are bird flu symptoms and signs?

Symptoms occur approximately two to eight days after exposure, on average. Infected people experience typical flu-like symptoms that may include

  • fever (above 38 C or 100.4 F),
  • cough (usually dry or nonproductive of sputum),
  • sore throat,
  • muscle aches,
  • nausea,
  • vomiting,
  • diarrhea,
  • headache,
  • joint pain,
  • lethargy,
  • nasal secretions (runny nose),
  • insomnia,
  • eye infections.

Children get similar symptoms. This viral infection can progress to pneumonia and even respiratory failure. Bird flu causes a very aggressive form of pneumonia (acute respiratory distress syndrome or ARDS) that is often fatal.

How do physicians diagnose bird flu?

Routine tests for human influenza A will be positive in patients with bird flu but are not specific for the avian virus. To make a specific diagnosis of bird flu, specialized tests are needed. In the United States, local health departments and the Centers for Disease Control and Prevention (CDC) can provide access to the specialized testing. The virus can be detected in sputum by several methods, including culture or polymerase chain reaction (PCR). Cultures should be done in laboratories that have an appropriate biosafety certification. PCR detects nucleic acid from the influenza A virus. Specialized PCR testing is available in reference laboratories to identify avian strains; the CDC is a primary source for available tests for the newest strains of bird flu and can identify the specific type of virus (for example, H5N1 or H7N9).

During and after infection with bird flu, the body makes antibodies against the virus. Blood tests can detect these antibodies, but this requires one sample at the onset of disease and another sample several weeks later. Thus, results are usually not available until the patient has recovered or died.

What is the treatment for bird flu?

Because of the small number of human cases, it has not been possible to conduct rigorous treatment trials for bird flu. The CDC suggests the best way to prevent bird flu is to avoid exposure whenever possible to birds and their feces. People are advised not to touch any ill appearing or dead birds. The CDC and the World Health Organization (WHO) currently recommend oseltamivir (Tamiflu) and zanamivir (Relenza) for the treatment and prevention of avian influenza a viruses. The U.S. government is currently stockpiling H5N1 vaccine in case the virus begins easy person-to-person transmission. Currently, there is no vaccine to protect against H7N9 types of bird flu.

Source: http://www.rxlist.com

Because of the small number of human cases, it has not been possible to conduct rigorous treatment trials for bird flu. The CDC suggests the best way to prevent bird flu is to avoid exposure whenever possible to birds and their feces. People are advised not to touch any ill appearing or dead birds. The CDC and the World Health Organization (WHO) currently recommend oseltamivir (Tamiflu) and zanamivir (Relenza) for the treatment and prevention of avian influenza a viruses. The U.S. government is currently stockpiling H5N1 vaccine in case the virus begins easy person-to-person transmission. Currently, there is no vaccine to protect against H7N9 types of bird flu.

Source: http://www.rxlist.com

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